In the last few decades a lot of research has been done in the field of plain bearings in general. Most of the investigations have been done in the field called “micro grooves” or “micro ramps” in at least one of the surfaces of the radial bearing partners. It consists of inserting micro geometrical modifications in the hydrodynamic bearing surface in order to improve its performance under actual operating conditions. But in the special field of radial bearings for crank-drives, which are operated under difficult operational conditions due to continuously changing load directions and load conditions, a deeper research in improving the radial plain bearings has not been performed.
Document U.S. Pat. No. 5,725,314 A refers to a hydrodynamic bearing including a cylindrical body having an inner wall and an outer wall, a plurality of gutters along the inner wall and a number of wedge-shaped recesses in fluid receiving communication with the gutters. Thus, the wedge-shaped recesses and the gutters form a number of micro grooves in one of the bearing surfaces. The wedge-shaped recesses has a wide portion along the circumference of the inner wall but none of the disclosed embodiments feature micro structures in the inner or outer bearing surface, which are only partly applied in the bearing surface, and the shown gutters and microgrooves lead to a decrease of maximal mechanical load.
Document U.S. Pat. No. 4,747,705 A discloses another hydrodynamic bearing having a plurality of pads on the inner bearing surface forming ramp shaped peaks. The bearing is optimized for high speed turbo machines which require special journal bearings to support their high speed rotating parts. Hydrodynamic bearings operate under the principle of hydrodynamic generation, wherein pressure is generated in the clearance between the bearing surface and the rotating part, such pressure producing a net load capacity and film stiffness. The hydrodynamic bearing herein disclosed is performed for special high speed applications and do not allow low rotating speeds and are optimized for about 40.000 rpm. Thus, a bearing having ramps in the bearing surface as herein disclosed are not applicable for crank-drive and in particular for supporting a crank-shaft in a crank-housing, because the bearing is not performed to provide a sufficient mechanical load.